This invention relates to valve actuators, and in particular to an automatic valve actuator for actuation of a rotary valve, especially a rotary butterfly valve, in response to a particular occurrence of a character such that immediate automatic opening or closing of the valve is desired.
It has been known to provide automatic valve actuators for causing immediate actuation of a valve in an emergency. Such valve actuators, as, for example, taught by this applicant in Lyons U.S. Pat. No. 4,275,754, are especially suited for ball valves which, when closed, are securely shut off and, when open, are securely open to passage. Such actuators, however, are not especially suited for use in connection with butterfly valves, which have a tendency to change relative position within a flowpath when fluid pressure is applied, as these actuators are devoid of a means of securely locking the valve in its actuated position. Such actuators also do not include means for ensuring that a valve is absolutely maintained in its fully closed position upon actuation, if, for example, such is its actuated position.
Other automatic valve actuators are incapable of effectively providing means for securely presetting the valve in a position other than fully open or fully closed. This disadvantage has prevented the pre-setting of butterfly valves in, for example, a half-open, flow rate-controlling position. It has, therefore, been necessary to employ two valve mechanisms: one for controlling flow rate and one for providing emergency actuation.